Sorry VHL, but you've got the wrong end of the stick.
VanHalenLover: if it has a balance and has a valid number,
If it has a balance it's not a credit card. Credit cards with a pre-paid balance are gift cards.
Here is Visa's page on them.
Yes, Visa and MC (and all the rest of the CC companies who retail Gift Cards) know which accounts are PRE-PAID and which are ISSUED WITH A LINE OF CREDIT. Yes, you use a Gift Card LIKE a credit card, and not a debit card (PIN), that doesn't change the fact that the card is PRE-PAID.
When you use a credit card, you are billed for the balance against your line of credit. When you use a gift card the amount is deducted from a pre-set, or pre-paid, balance. This is why they can charge you interest (7% - 24%!!!) on a Credit Card for any outstanding balance... you are spending their money until you repay them.
Visa:
How to use your card
Using your Visa Gift card for a purchase is similar to using a credit card. When you are ready to pay, give the card to the cashier and ask to sign the purchase receipt.
If asked, swipe the card through the keypad, push the "credit" button and sign the receipt. Note: Most Visa Gift cards do not come with a PIN, therefore, you should not push "debit". This will cause your transaction to be declined.
Each time your card is used for a purchase, that amount is automatically deducted from your balance. It is recommended that you know your balance before making a purchase because many merchants will not be able to provide that information. See details below.
The Visa Gift card is 'non-reloadable', so additional money cannot be added to the balance of the card. The card does not offer a line of credit like a credit card. The initial value available for use is determined by the person who purchased the card.
.... emphasis mine.
Believe me when I tell you that the CC companies can tell you immediately if the card you're using is PRE-PAID or not. This information is relayed to the merchant in real time (our VeriFone Vx570 is never wrong.)
It would be very simple for WGT to verify, via Merchant Services, the difference between the Gift Cards and the Credit Cards.